AIR COMPRESSOR GOVERNORThis article was submitted by John Kee.
Webmaster Note - I recently had a problem with my air.  On initial startup, the air would not build up above 70 psi, and would fall rapidly with application of the air horn or air brakes.  Sometimes, dumping the air and restarting would restore normal operation.  FL San Antonio diagnosed this as a faulty air compressor, but based on John's article, I think it was probably just the governor.  Based on John's experience with two failed governors, I now carry a spare governor.  Thanks to John for this excellent article.  John has also provided the excellent pictures along with his article.  Click on a thumbnail for a larger view.
The air governor is located on the rear of the air pump on the curb side of the engine up next to the front (rear of the coach.   Note the belt pulleys, etc).
It is mounted on the pump with two bolts that need an allen wrench to remove them. Also, there are two small air lines running to the governor that will have to be removed (don't get the air lines crossed).
VERY IMPORTANT!To change the governor, first and foremost, completely bleed the air from the system by pumping on the brake pedal until there is no pressure on the guages.
Remove the air lines from the governor and don't get them mixed up (you may want to tag them).  Remove the two screws with an allen wrench and remove the air governor.  Here is a picture of a new governor.
On the outside where you have more room, examine the governor and remove the two fittings that go to the air lines and place them on the new governor. Remove the plugs on the old governor and install on the new governor, insuring that they are installed exactly as they came out of the old governor. Proir to installing the plugs, use teflon tape or other sealer to create a tight seal. Also put teflon tape or other sealer on the air line fittings.
Once you are ready to reinstall the governor, place the gasket (supplied with the new governor) and screws on the governor and bolt in place.  Reinstall the air lines and you're ready to go!!!
Most of the above is self-explanatory, once you see the governor and recognize what it does.
The governor is adjustable as to air pressure on the system, as shown in this photo.   The screw will adjust the air pressure up or down. I had approx 130 lbs showing on my guages when the governor went out.
Part Number for the governor: Bendix 275491, which you can pick up at any large truck facility.
Doing this the other week saved me from a tow and a long wait at wherever I would have to had it fixed!!